Many mattresses incorporate springs into the mattress innercore to provide mattress resiliency. At the same time, foam mattresses are becoming more popular with a certain set of mattress consumers because their compressive properties differ significantly from standard spring-based innercore mattresses. The mechanical deflection properties of foam are complex. These properties depend upon the geometry of the cells that make up the foam and the properties of the polymer making up the foams structural elements. Cell size and polymer density also play a role. Further complicating the response is that elements of the foam that effect its mechanical response can vary depending as a function of applied load. Thus, foam, such as polyurethane foam, typically has a non-linear deflection response, that is dependent on the particular characteristics of the foam. One example of a deflection response for a foam block is presented in FIG. 7.3 of Dow Polyurethanes. Flexible Foams, Herrington et al., Dow Chemical Company, 2nd Edition (1997). This figure illustrates the complex deflection response mechanics provided by foam cores.
Steel coil springs of conventional symmetric helical design have a well know linear spring response. Non-linear spring coils are also known that have non-linear responses to applied loads, by having coils of progressively smaller radius that present varying response to a load of increasing force. However, non-linear springs lack the complex dynamic response of a cellular foam block.
Accordingly, there remains a need in the art for a spring inner-core that provides a deflection response that is comparable to the response of foam. Therefore, a method for providing the compressive properties of foam with a spring-based mattress or innercore is desirable.